Organic el display unit and electronic apparatus

ABSTRACT

An organic EL display unit applying a bottom-emission structure which takes light emitted from organic EL devices from the reverse side of a substrate on which pixel circuits are formed, includes: a color filter formed on the pixel circuit; and a metal wiring formed so as to surround the periphery of the color filter, wherein the metal wiring is set to an anode potential of the organic EL device.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation application of U.S. patent application Ser. No.13/313,743, filed Dec. 7, 2011, which claims priority to Japanese PatentApplication JP 2011-000940 filed with the Japanese Patent Office on Jan.6, 2011, the entire contents of which being incorporated herein byreference.

FIELD

The present disclosure relates to an organic EL display unit and anelectronic apparatus, and particularly relates to an organic EL displayunit using a bottom-emission method as a method of taking light emittedfrom organic EL devices, and an electronic apparatus having the organicEL display unit.

BACKGROUND

As one of flat-panel type display units, there is a display unit using aso-called current-driven electro-optic device in which light emissionluminance varies in accordance with a current value flowing in thedevice as a light emitting portion (light emitting device) of a pixel.An organic EL device is known as the current-driven electro-opticdevice, which uses electroluminescence (EL) of an organic material andutilizes a phenomenon that an organic thin film emits light when anelectric field is impressed.

An organic EL display unit using the organic EL device as the lightemitting portion of the pixel has the following characteristics. Thatis, the organic EL device consumes low power as it can be driven by anapplication voltage of 10V or less. As the organic EL device is aself-luminous device, visibility of images is higher than a liquidcrystal display unit, and further, the organic EL device can be light inweight as well as can be thin in thickness as an illumination membersuch as a backlight is not necessary. Moreover, response speed isextremely high in the organic EL device, which is several μsec, noresidual image is generated at the time of displaying moving pictures.

In the organic EL display unit, a bottom-emission method is known as amethod of taking light emitted by the organic EL devices, in which lightis taken from the backside of a substrate on which pixel circuits eachincluding a thin-film transistor (TFT), a capacitor device and so on areformed (for example, see JP-A-2008-218427 (Patent Document 1)). Whencolor filters are mounted on the bottom-emission type organic EL displayunit, for example, a structure of forming color filters on the pixelcircuits formed on the substrate is applied.

SUMMARY

In the bottom-emission type (structure) organic EL display unit,internal resistance of the color filter may vary according to a materialof the color filter by receiving light emission of a self-pixel whenlight emitted from the organic EL device is transmitted through thecolor filter. The pixel circuit is formed under the color filter in thebottom-emission type organic EL display unit, therefore, variation ofinternal resistance in the color filter affects circuit operations ofthe pixel circuit when the internal resistance of the color filtervaries.

In view of the above, it is desirable to provide an organic EL displayunit and an electronic apparatus having the organic EL display unitwhich can suppress adverse effect caused by variation of internalresistance of the color filter with respect to circuit operations of thepixel circuit when applying the bottom emission method.

An embodiment of the present disclosure is directed to an organic ELdisplay unit applying a bottom-emission structure which takes lightemitted from organic EL devices from the reverse side of a substrate onwhich pixel circuits are formed, which includes a color filter formed onthe pixel circuit and a metal wiring formed so as to surround theperiphery the color filter, in which the metal wiring is set to an anodepotential of the organic EL device.

In the organic EL display unit having the above configuration, the colorfilter can be equivalently shown as a parallel circuit including acapacitive component and an impedance component connected in parallel.Then, when the periphery of the color filter is surrounded by the metalwiring set to the anode potential, both terminals of the equivalentcircuit of the color filter have electrically the same potential.Therefore, even when internal resistance of the color filter varies byreceiving light emission of a self-pixel, the variation of the internalresistance of the color filter does not affect circuit operations of thepixel circuit as both terminals of the equivalent circuit have the samepotential.

According to the embodiment of the present disclosure, when the internalresistance of the color filter varies by receiving light emission of theself-pixel in the organic EL display unit applying the bottom-emissionmethod, adverse effect caused by variation of internal resistance of thecolor filter with respect to the circuit operations of the pixel circuitcan be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram showing an outline of aconfiguration of an active-matrix organic EL display unit to which thepresent disclosure is applied;

FIG. 2 is a circuit diagram showing an example of a specific circuitconfiguration of a pixel (pixel circuit);

FIG. 3 is a timing waveform diagram for explaining basic circuitoperations of the organic EL display unit to which the presentdisclosure is applied;

FIGS. 4A to 4D are operation explanation diagrams (No. 1) of basiccircuit operations of the organic EL display unit to which the presentdisclosure is applied;

FIGS. 5A to 5D are operation explanation diagrams (No. 2) of basiccircuit operations of the organic EL display unit to which the presentdisclosure is applied;

FIGS. 6A and 6B are characteristic graphs for explaining problems causedby variation of a threshold voltage V_(th) of a drive transistor (FIG.6A) and problems caused by variation of a mobility μ of the drivetransistor;

FIG. 7 is a cross-sectional view showing an example of a bottom-emissionstructure;

FIG. 8 is a circuit diagram showing an equivalent circuit of a colorfilter;

FIG. 9 is a timing waveform diagram for explaining problems caused byvariation of internal resistance of the color filter;

FIG. 10 is a plan view showing an example of a pixel configuration in anorganic EL display unit according to an embodiment;

FIG. 11 is an arrow cross-sectional view taken along A-A′ line of FIG.10;

FIG. 12 is an arrow cross-sectional view taken along B-B′ line of FIG.10;

FIG. 13 is a circuit diagram showing an equivalent circuit of the colorfilter for explaining operation and effect of the embodiment;

FIG. 14 is a perspective view showing appearance of a television set towhich the present disclosure is applied;

FIGS. 15A and 15B are perspective views showing appearance of a digitalcamera to which the present disclosure is applied, in which FIG. 15A isa perspective view seen from the front side and FIG. 15B is aperspective view seen from the back side;

FIG. 16 is a perspective view showing appearance of a notebook personalcomputer to which the present disclosure is applied;

FIG. 17 is a perspective view showing appearance of a video camera towhich the present disclosure is applied; and

FIGS. 18A to 18G are appearance views of a cellular phone device towhich the present disclosure is applied, in which FIG. 18A is a frontview in an opened state, FIG. 18B is a side view thereof, FIG. 18C is afront view in a closed state, FIG. 18D is a left-side view, FIG. 18E isa right-side view, FIG. 18F is an upper surface view and FIG. 18G is abottom surface view.

DETAILED DESCRIPTION

Hereinafter, a mode for carrying out the present disclosure (hereinafterreferred to as “embodiment”) will be explained in detail with referenceto the drawings. The explanation will be made in the following order.

1. Organic EL display unit to which the present disclosure is applied

-   -   1-1. System configuration    -   1-2. Basic circuit operations    -   1-3. Bottom-emission structure    -   1-4. Problems caused by variation of internal resistance of a        color filter

2. Explanation of an embodiment

-   -   2-1. Pixel configuration according to the embodiment    -   2-2. Operation and effect of the embodiment

3. Application example

4. Electronic apparatus

1. Organic EL Display Unit to which the Present Disclosure is Applied[1-1. System Configuration]

FIG. 1 is a system configuration diagram showing an outline of aconfiguration of an active-matrix organic EL display unit to which thepresent disclosure is applied.

The active-matrix organic EL display unit is a display unit controllingelectric current flowing in an organic EL device which is acurrent-driven electro-optic device by an active device, for example, aninsulating-gate field effect transistor provided in the same pixel wherethe organic EL device is provided. As an insulating-gate field effecttransistor, a TFT (thin-film transistor) is typically used.

As shown in FIG. 1, an organic EL display unit 10 according to theapplication example includes plural pixels 20 having organic EL devices,a pixel array section 30 in which the pixels 20 are two-dimensionallyarranged in a matrix state and a drive circuit unit arranged in theperiphery of the pixel array section 30. The drive circuit unit includesa writing scanning circuit 40, a power supply scanning circuit 50, asignal output circuit 60 and so on, which drives respective pixels 20 inthe pixel array section 30.

Here, when the organic EL display unit 10 supports color display, onepixel (unit pixel) to be a unit for forming a color image includesplural sub-pixels, and each sub-pixel corresponding to the pixel 20 ofFIG. 1. More specifically, one pixel includes three sub-pixels whichare, for example, a sub-pixel emitting red (R) light, a sub-pixelemitting green (G) light and a sub-pixel emitting blue (B) light in thedisplay unit supporting color display.

However, one pixel is not limited to be formed by a combination ofsub-pixels of three primary colors RGB but it is also possible to addsub-pixels of one or plural colors to the sub-pixels of three primarycolors to form one pixel. More specifically, for example, it is possibleto add a sub-pixel emitting white (W) light to form one pixel forimproving luminance or to add at least one sub-pixel emitting light of acomplementary color to form one pixel for expanding a color reproductionrange.

In the pixel array section 30, scanning lines 31 ₁ to 31 _(m) and powersupply lines 32 ₁ to 32 _(m) are arranged at respective pixel rows alonga row direction (arrangement direction of pixels in pixel rows) withrespect to arrangement of pixels 20 of m-rows and n-columns.Furthermore, signal lines 33 ₁ to 33 _(n) are arranged at respectivepixel columns along a column direction (arrangement direction of pixelsin pixel columns) with respect to arrangement of pixels 20 of m-rows andn-columns.

The scanning lines 31 ₁ to 31 _(m) are respectively connected to outputterminals of corresponding rows of the writing scanning circuit 40. Thepower supply lines 32 ₁ to 32 _(m) are respectively connected to outputterminals of corresponding rows of the power supply scanning circuit 50.The signal lines 33 ₁ to 33 _(n) are respectively connected to outputterminals of corresponding columns of the signal output circuit 60.

The pixel array section 30 is normally formed on a transparentinsulating substrate such as a glass substrate. Thus, the organic ELdisplay unit 10 has a flat type panel structure. The drive circuits ofrespective pixels 20 in the pixel array section 30 can be formed byusing an amorphous silicon TFT or a low-temperature polysilicon TFT.When using the low-temperature polysilicon TFT, the writing scanningcircuit 40, the power supply scanning circuit 50 and the signal outputcircuit 60 can be also mounted on a display panel (substrate) 70 onwhich the pixel array section 30 is formed as shown in FIG. 1.

The writing scanning circuit 40 includes a shift register circuitsequentially shifting (transfers) a start pulse “sp” in synchronizationwith a clock pulse “ck” and so on. The writing scanning circuit 40sequentially supplies writing scanning signals WS (WS₁ to WS_(m)) to thescanning lines 31 (31 ₁ to 31 _(m)) when writing a signal voltage of avideo signal to respective pixels 20 in the pixel array section 30,thereby sequentially scanning (line-sequential scanning) respectivepixels 20 in the pixel array section 30 on a row basis.

The power supply scanning circuit 50 includes the shift register circuitsequentially shifting the start pulse “sp” in synchronization with aclock pulse “ck” and so on. The power supply scanning circuit 50supplies power supply potentials DS (DS₁ to DS_(m)) which can beswitched between a first power supply potential V_(ccp) and a secondpower supply potential V_(ini) which is lower than the first powersupply potential V_(ccp) to the power supply lines 32 (32 ₁ to 32 _(m))in synchronization with the line sequential scanning by the writingscanning circuit 40. As described later, light emission/non-lightemission of pixels 20 is controlled by switching between V_(ccp)/V_(ini)of the power supply potentials DS.

The signal output circuit 60 selectively outputs a signal voltageV_(sig) of a video signal (hereinafter may be referred to as merely“signal voltage”) corresponding to luminance information supplied from asignal supply source (not shown) and a reference voltage V_(ofs). Here,the reference signal V_(ofs) is a potential to be a reference of thesignal voltage V_(sig) of the video signal (for example, a potentialcorresponding to a black-level of the video signal) and used at the timeof later-described threshold correction processing.

The signal voltages V_(sig)/reference voltage V_(ofs) outputted from thesignal output circuit 60 are written in respective pixels 20 in thepixel array section 30 through the signal lines 33 (33 ₁ to 33 _(n)) ona pixel-row basis selected by scanning by the writing scanning circuit40. That is, the signal output circuit 60 applies a driving mode ofline-sequential writing in which the signal voltage V_(sig) is writtenon a row (line) basis.

(Pixel Circuit)

FIG. 2 is a circuit diagram showing an example of a specific circuitconfiguration of the pixel (pixel circuit) 20. A light emitting portionof the pixel 20 includes an organic EL device 21 which is acurrent-driven electro-optic device in which light emission luminancevaries in accordance with a current value flowing in the device.

As shown in FIG. 2, the pixel 20 includes the organic EL device 21 and adrive circuit driving the organic EL device 21 by allowing electriccurrent to flow in the organic EL device 21. A cathode electrode of theorganic EL device 21 is connected to a common power supply line 34 wiredto all pixels in common (so-called plane wiring).

The drive circuit driving the organic EL device 21 includes a drivetransistor 22, a write transistor 23 and a storage capacitor 24. As thedrive transistor 22 and the write transistor 23, an N-channel TFT can beused. However, a combination of a conductive type of the drivetransistor 22 and the write transistor 23 is merely an example and isnot limited to the combination.

One electrode (source/drain electrode) of the drive transistor 22 isconnected to an anode electrode of the organic EL device 21 and theother electrode (drain/source electrode) thereof is connected to thepower supply line 32 (32 ₁ to 32 _(m)).

One electrode (source/drain electrode) of the write transistor 23 isconnected to the signal line 33 (33 ₁ to 33 n) and the other electrode(drain/source electrode) thereof is connected to a gate electrode of thedrive transistor 22. A gate electrode of the write transistor 23 isconnected to the scanning line 31 (31 ₁ to 31 _(m)).

In the drive transistor 22 and the write transistor 23, one electrodecorresponds to metal wiring electrically connected to a source/drainregion and the other electrode corresponds to metal wiring electricallyconnected to a drain/source region. One electrode can be the sourceelectrode as well as the drain electrode and the other electrode can bethe drain electrode as well as the source electrode according to thepotential relation between one electrode and the other electrode.

One electrode of the storage capacitor 24 is connected to the gateelectrode of the drive transistor 22 and the other electrode thereof isconnected to the other electrode of the drive transistor 22 and theanode electrode of the organic EL device 21.

The drive circuit of the organic EL device 21 is not limited to thecircuit configuration having two transistors which are the drivetransistor 22 and the write transistor 23 and one capacitor device whichis the storage capacitor 24. That is, it is possible to apply a circuitconfiguration, as an example, in which an auxiliary capacitor isprovided according to need, which compensates for the lack of capacityin the organic EL device 21 by connecting one electrode to the anodeelectrode of the organic EL device 21 and connecting the other electrodeto a fixed potential.

In the pixel 20 having the above configuration, the write transistor 23becomes conductive in response to a high-active write scanning signal WSapplied to the gate electrode from the writing scanning circuit 40through the scanning line 31. Thus, the write transistor 23 performssampling of the signal voltage V_(sig) of the video signal correspondingto luminance information or the reference voltage V_(ofs) supplied fromthe signal output circuit 60 through the signal line 33 and writes thevoltage in the pixel 20. The written signal voltage V_(sig) or thereference signal V_(ofs) is applied to the gate electrode of the drivetransistor 22 as well as stored in the storage capacitor 24.

The drive transistor 22 operates in a saturation region in a state whereone electrode is the drain electrode and the other electrode is thesource electrode when the power supply potential DS of the power supplyline 32 (32 ₁ to 32 _(m)) is in the first power supply potentialV_(ccp). Thus, the drive transistor 22 drives the organic EL device 21to emit light by current driving by receiving current supply from thepower supply line 32. More specifically, the drive transistor 22operates in the saturation region to thereby supply drive current of acurrent value corresponding to a voltage value of the signal voltageV_(sig) stored in the storage capacitor 24 and drives the organic ELdevice 21 by current to emit light.

The drive transistor 22 further operates as a switching transistor in astate where one electrode is the source electrode and the otherelectrode is the drain electrode when the power supply potential DS isswitched from the first power supply potential V_(ccp) to the secondpower supply potential V_(ini). Thus, the drive transistor 22 stopssupply of drive current to the organic EL device 21 and allows theorganic EL device 21 to be in a non-light emitting state. That is, thedrive transistor 22 also has a function of a transistor controllinglight emission/non-light emission of the organic EL device 21.

According to the switching operation of the drive transistor 22, aperiod during which the organic EL device 21 does not emit light(non-light emission period) is provided to thereby control a ratio(duty) of a light emission period and the non-light emission period ofthe organic EL device 21. The residual image blur caused by lightemission of the pixel over one display frame period can be reduced bythe duty control, therefore, it is possible to especially improvequality of moving pictures.

In the first and second power supply potentials V_(ccp) and V_(ini)selectively supplied from the power supply scanning circuit 50 throughthe power supply line 32, the first power supply potential V_(ccp) is apower supply potential for supplying drive current for driving theorganic EL device 21 to emit light to the drive transistor 22. Thesecond power supply potential V_(ini) is a power supply potential forapplying reverse bias to the organic EL device 21. The second powersupply potential V_(ini) is set to a potential lower than the referencevoltage V_(ofs), for example, a potential lower than V_(ofs)−V_(th) whena threshold voltage of the drive transistor 22 is V_(th), preferably apotential sufficiently lower than V_(ofs)−V_(th).

[1-2. Basic Circuit Operations]

Subsequently, basic circuit operations of the organic EL display unit 10having the above configuration will be explained with reference tooperation explanation diagrams of FIGS. 4A to 4D and FIGS. 5A to 5Dbased on a timing waveform diagram of FIG. 3. In the operationexplanation diagrams of FIGS. 4A to 4D and FIGS. 5A to 5D, the writetransistor 23 is shown by a symbol of a switch for simplifying thedrawings. Additionally, an equivalent capacitor 25 of the organic ELdevice 21 is also shown.

In the timing waveform diagram of FIG. 3, variations of the potential(writing scanning signal) WS of the scanning line 31, the potential(power supply potential) DS of the power supply line 32, the potential(V_(sig)/V_(ofs)) of the signal line 33, the gate potential Vg and thesource potential Vs of the drive transistor 22 are respectively shown.

(Light Emission Period in a Previous Display Frame)

In the timing waveform diagram of FIG. 3, a period before a time point“t11” is a light emission period of the organic EL device 21 in aprevious display frame. In the light emission period in the previousdisplay frame, the potential DS of the power supply line 32 is in thefirst power supply potential (hereinafter referred to as “highpotential”) V_(ccp), and the write transistor 23 is in thenon-conductive state.

At this time, the drive transistor 22 is designed to operate in thesaturation region. Thus, a drive current (drain-source current) I_(ds)corresponding to the gate-source voltage V_(gs), of the drive transistor22 is supplied from the power supply line 32 to the organic EL device 21through the drive transistor 22 as shown in FIG. 4A. Therefore, theorganic EL device 21 emits light with luminance corresponding to acurrent value of the drive current I_(ds).

(Threshold Correction Preparation Period)

At the time point “t11”, the line-sequential scanning enters a newdisplay frame (current display frame). Then, the potential DS of thepower supply line 32 is switched from the high potential V_(ccp) to thesecond power supply potential (hereinafter, referred to as “lowpotential”) V_(ini) which is sufficiently lower than V_(ofs)−V_(th) withrespect to the reference voltage V_(ofs) of the signal line 33 as shownin FIG. 4B.

Here, a threshold voltage of the organic EL device 21 is V_(thel) and apotential of the common power supply line 34 (cathode potential) isV_(cath). At this time, when the low potential V_(ini) is lower thanV_(thel)+V_(cath) the source potential Vs of the drive transistor 22 isapproximately equal to the low potential V_(ini), therefore, the organicEL device 21 becomes in the reverse bias state and stops light emission.

Next, when the potential WS of the scanning line 31 is changed from thelow potential side to the high potential side at a time point “t12”, thewrite transistor 23 becomes conductive as shown in FIG. 4C. As thereference voltage V_(ofs) is supplied from the signal output circuit 60to the signal line 33 at this time, the gate potential Vg of the drivetransistor 22 becomes in the reference voltage V_(ofs). The sourcevoltage Vs of the drive transistor 22 is in the potential sufficientlylower than the reference voltage V_(ofs), namely, in the low potentialV_(ini).

At this time, the gate-source voltage V_(g), of the drive transistor 22is V_(ofs)−V_(ini). Here, it is difficult to perform later-describedthreshold correction processing unless V_(ofs)−V_(ini) is higher thanthe threshold voltage V_(th) of the drive transistor 22, therefore, itis necessary to set the potential relation to V_(ofs)−V_(ini)>V_(th).

As described above, the processing of fixing the gate potential Vg ofthe drive transistor 22 to the reference voltage V_(ofs) as well asfixing (determining) the source potential Vs to the low potentialV_(ini) to be initialized is preparation processing (thresholdcorrection preparation) before performing later-described thresholdcorrection processing (threshold correction operation). Therefore, thereference voltage V_(ofs) and the low potential V_(ini) are respectiveinitialization potentials of the gate potential Vg and the sourcepotential Vs of the drive transistor 22.

(Threshold Correction Period)

Next, when the potential DS of the power supply line 32 is switched fromthe low potential V_(ini) to the high potential V_(ccp) at a time point“t13” as shown in FIG. 4D, the threshold correction processing isstarted in a state where the gate potential Vg of the drive transistor22 is maintained to the reference voltage V_(ofs). That is, the sourcepotential Vs of the drive transistor 22 starts to increase toward apotential obtained by subtracting the threshold voltage Vth of the drivetransistor 22 from the gate potential Vg.

Here, processing of changing the source potential Vs toward thepotential obtained by subtracting the threshold voltage Vth of the drivetransistor 22 from the initialization potential V_(ofs) based on theinitialization potential V_(ofs) of the gate potential Vg of the drivetransistor 22 is referred to as the threshold correction processing forconvenience. As the threshold correction processing proceeds, thegate-source voltage V_(gs) of the drive transistor 22 finally convergesto the threshold voltage V_(th) of the drive transistor 22. The voltagecorresponds to the threshold voltage V_(th) is stored in the storagecapacitor 24.

In the period during which the threshold correction processing isperformed (threshold correction period), the potential V_(cath) of thecommon power supply line 34 is set so that the organic EL device 21 isin a cutoff state for allowing electric current flow only in the storagecapacitor 24 side and not to flow in the organic EL device 21 side.

Next, when the potential WS of the scanning line 31 is changed to thelow potential side at a time point “t14”, the write transistor 23becomes non-conductive as shown in FIG. 5A. At this time, the gateelectrode of the drive transistor 22 is electrically cut off from thesignal line 33 and made to be in a floating state. However, the drivetransistor 22 is in the cutoff state as the gate-source voltage V_(g),is equal to the threshold voltage V_(th) of the drive transistor 22.Therefore, the drain-source current I_(ds) does not flow in the drivetransistor 22.

(Signal Writing & Mobility Correction Period)

Next, the potential of the signal line 33 is switched from the referencevoltage V_(ofs) to the signal voltage V_(sig) of the video signal at atime point “t15” as shown in FIG. 5B. Subsequently, when the potentialWS of the scanning line 31 is changed to the high potential side at atime point “t16”, the write transistor 23 becomes conductive andperforms sampling of the signal voltage V_(sig) of the video signal tobe written in the pixel 20 as shown in FIG. 5C.

The gate potential Vg of the drive transistor 22 will be the signalvoltage V_(sig) by the writing of the signal voltage V_(sig) by thewrite transistor 23. Then, the threshold voltage V_(th) of the drivetransistor 22 is cancelled out by the voltage corresponding to thethreshold voltage V_(th) stored in the storage capacitor 24 when thedrive transistor 22 is driven by the signal voltage V_(sig) of the videosignal. The details of the principle of threshold cancellation will bedescribed later.

At this time, the organic EL device 21 is in the cutoff state(high-impedance state). Therefore, electric current flowing from thepower supply line 32 to the drive transistor 22 (drain-source currentI_(ds)) in accordance with the signal voltage V_(sig) of the videosignal flows into the equivalent capacitor 25 of the organic EL device21. As a result, charge of the equivalent capacitor 25 of the organic ELdevice 21 is started.

When the equivalent capacitor 25 of the organic EL device 21 is charged,the source potential Vs of the drive transistor 22 is increased with alapse of time. At this point, variations of the threshold voltage V_(th)of the drive transistor in respective pixels have been already cancelledout, and the drain-source current I_(ds) of the drive transistor 22depends on a mobility μ of the drive transistor 22. The mobility μ ofthe drive transistor 22 is the mobility of a semiconductor thin filmforming a channel of the drive transistor 22.

Here, assume that the ratio of the voltage V_(gs) stored in the storagecapacitor 24 with respect to the signal voltage V_(sig) of the videosignal, namely, a write gain G is 1 (desired value). Then, when thesource potential Vs of the drive transistor 22 is increased to apotential of V_(ofs)−V_(th)+ΔV, the gate-source voltage V_(gs) of thedrive transistor 22 will be V_(sig)−V_(ofs)+V_(th)−ΔV.

That is, the increased amount ΔV of the source potential Vs of the drivetransistor 22 works so as to be subtracted from the voltage stored inthe storage capacitor 24 (V_(sig)−V_(ofs)+V_(th)), in other words, so asto discharge the stored charges of the storage capacitor 24. In short,the increased amount ΔV of the source potential Vs means that negativefeedback is given to the storage capacitor 24. Therefore, the increasedamount ΔV of the source potential Vs is a feedback amount of thenegative feedback.

As described above, the negative feedback is given to the gate-sourcevoltage Vgs by the feedback amount ΔV corresponding to the drain-sourcecurrent I_(ds) flowing in the drive transistor 22, thereby cancellingout dependence of the drain-source current I_(ds) of the drivetransistor 22 with respect to the mobility μ. The processing ofcancellation corresponds to mobility correction processing whichcorrects variations of the mobility μ of the drive transistor 22 inrespective pixels.

More specifically, the drain-source current I_(ds) is increased as asignal amplitude V_(in) (=V_(sig)−V_(ofs)) of the video signal writtenin the gate electrode of the drive transistor 22 becomes higher,therefore, an absolute value of the feedback amount ΔV of negativefeedback is also increased. Thus, the mobility correction processingcorresponding to the light emission luminance level is performed.

When the signal amplitude V_(in) of the video signal is fixed, theabsolute value of the feedback amount ΔV of negative feedback isincreased as the mobility μ of the drive transistor 22 becomes higher,therefore, variations of the mobility μ in respective pixels can becancelled. Thus, the feedback amount ΔV of negative feedback can be alsodefined as a correction amount of the mobility correction processing.The details of the principle of mobility correction will be describedlater.

(Light Emission Period)

Next, when the potential WS of the scanning line 31 is changed to thelow potential side at a time point “t17”, the write transistor 23becomes in the non-conductive state as shown in FIG. 5D. Accordingly,the gate electrode of the drive transistor 22 is electrically cut offfrom the signal line 33 and becomes in the floating state.

Here, when the gate electrode of the drive transistor 22 is in afloating state, the gate potential Vg varies in conjunction with thevariation of the source potential Vs of the drive transistor 22 as thestorage capacitor 24 is connected between the gate and the source of thedrive transistor 22. An operation in which the gate potential Vg of thedrive transistor 22 varies in conjunction with the variation of thesource potential Vs as described above is defined as a bootstrapoperation by the storage capacitor 24.

When the gate electrode of the drive transistor 22 is in the floatingstate and the drain-source current I_(ds) of the drive transistor 22starts to flow in the organic EL device 21 at the same time, an anodepotential of the organic EL device 21 is increased according to thecurrent I_(ds).

Then, when the anode potential of the organic EL device 21 exceedsV_(thel)+V_(cath), the organic EL device 21 starts to emit light asdrive current starts to flow in the organic EL device 21. The increaseof the anode potential of the organic EL device 21 is nothing less thanthe increase of the source potential Vs of the drive transistor 22. Whenthe source potential Vs of the drive transistor 22 is increased, thegate potential Vg of the drive transistor 22 is increased in conjunctionof the source potential Vs due to the bootstrap operation by the storagecapacitor 24.

At this time, when assuming that a bootstrap gain is 1 (desired value),the increased amount of the gate potential Vg is equal to the increasedamount of the source potential Vs. Therefore, the gate-source voltageV_(g), of the drive transistor 22 is maintained to be constant atV_(sig)−V_(ofs)+V_(th)−ΔV during the light emission period. Then, thepotential of the signal line 33 is switched from the signal voltageV_(sig) of the video signal to the reference voltage V_(ofs) at a timepoint “t18”.

In the series of circuit operations explained as the above, respectiveprocessing operations of the threshold correction preparation, thethreshold correction, the writing of the signal voltage V_(sig) (signalwriting) and the mobility correction are executed during one horizontalscanning period (1H). The respective processing operations of the signalwriting and the mobility correction are executed in parallel during aperiod between the time points “t16” and “t17”.

(Divided Threshold Correction)

The case of applying the drive method of executing the thresholdcorrection processing just once has been explained as an example here,however, the drive method is just an example and is not limited to this.For example, it is possible to apply a drive method, so called a drivemethod of a divided threshold correction, in which the thresholdcorrection processing is additionally performed plural times separatelyover plural horizontal scanning periods preceding to the 1H periodduring which the threshold correction processing is performed with themobility correction and the signal writing processing.

According to the drive method of the divided threshold correction,sufficient time can be secured as the threshold correction periods overplural horizontal scanning periods even when time to be assigned to onehorizontal scanning period is reduced due to the increase of pixelsaccompanied by high definition of the device. Thus, the time can besecured as the threshold correction periods even when the time to beassigned to one horizontal scanning period is reduced, therefore, thethreshold correction processing can be positively executed.

(Principle of Threshold Cancellation)

Here, the principle of threshold cancellation (namely, thresholdcorrection) of the drive transistor 22 will be explained. The drivetransistor 22 operates as a constant current source as it is designed tobe operated in the saturation region. Thus, the constant drain-sourcecurrent (drive current) I_(ds) given by the following expression (1) issupplied to the organic EL device 21 from the drive transistor 22.

I _(ds)=(1/2)·μ(W/L)C _(ox)(V _(gs) −V _(th))²  (1)

Here, W represents a channel width of the drive transistor 22, Lrepresents a channel length and C_(ox) represents a gate capacitance pera unit area.

FIG. 6A shows characteristics between the drain-source current I_(d)sand the gate-source voltage V_(gs) in the drive transistor 22. As shownin a characteristic graph of FIG. 6A, if cancellation processing(correction processing) with respect to variations of the thresholdvoltage Vth of the drive transistor 22 in respective pixels is notperformed, the drain-source current Ids corresponding to the gate-sourcevoltage V_(gs) will be I_(ds1) when the threshold voltage V_(th) isV_(th1).

When the threshold voltage V_(th) is V_(th2) (V_(th2)>V_(th1)), thedrain-source current I_(ds) corresponding to the same gate-sourcevoltage V_(gs) will be I_(ds2) I_(ds2)<I_(ds1)). That is, when thethreshold voltage V_(th) of the drive transistor 22 varies, thedrain-source current I_(ds) also varies even when the gate-sourcevoltage V_(gs) is fixed.

On the other hand, the gate-source voltage V_(gs) of the drivetransistor 22 during light emission is V_(sig)−V_(ofs)+V_(th)−ΔV in thepixel (pixel circuit) 20 having the above configuration as describedabove. Thus, when the above is substituted into the expression (1), thedrain-source current I_(ds) is represented by the following expression(2).

I _(ds)=(1/2)·μ(W/L)C _(ox)(V _(sig) −V _(ofs) −ΔV)²  (2)

That is, a term of the threshold voltage V_(th) of the drive transistor22 is cancelled out, and the drain-source current I_(ds) supplied fromthe drive transistor 22 to the organic EL device 21 does not depend onthe threshold voltage V_(th) of the drive transistor 22. As a result,the drain-source current I_(ds) does not vary even when the thresholdvoltage V_(th) of the drive transistor 22 varies in respective pixelsdue to variations in manufacturing processes of the drive transistor 22,variations with time and so on, therefore, light emission luminance ofthe organic EL device 21 can be maintained to be constant.

(Principle of Mobility Correction)

Next, the principle of mobility correction of the drive transistor 22will be explained. FIG. 6B shows characteristic curves obtained bycomparing a pixel A the drive transistor 22 of which has relatively highmobility μ with a pixel B the drive transistor 22 of which hasrelatively low mobility μ. When the drive transistor 22 is made of apolysilicon thin transistor and the like, it is inevitable that themobility μ varies between pixels such as in the pixel A and the pixel B.

Let us consider the case, for example, where the signal amplitude V_(in)(=V_(sig)−V_(ofs)) in the same level is written to the gate electrodesof the drive transistors 22 in both pixels A and B in a state in whichthe mobility μ varies between the pixel A and the pixel B. In this case,if no correction of the mobility μ is made, large difference occursbetween a drain-source current I_(ds1)′ flowing in the pixel A havinghigher mobility μ and a drain-source current I_(ds2)′ flowing in thepixel B having lower mobility μ. When the large difference occurs in thedrain-source current I_(ds) between pixels due to variations of mobilityμ in respective pixels as described above, uniformity of the screen isreduced.

Here, as apparent from the transistor characteristic expression of theexpression (1), the drain-source current I_(ds) is increased when themobility μ is high. Therefore, the higher the mobility μ is, the largerthe feedback amount ΔV in negative feedback becomes. As shown in FIG.6B, a feedback amount ΔV₁ of the pixel A having high mobility μ islarger than a feedback amount ΔV₂ of the pixel B having low mobility μ.

Thus, when negative feedback is given to the gate-source voltage V_(gs)with the feedback amount ΔV corresponding to the drain-source currentI_(ds) of the drive transistor 22 by the mobility correction processing,the negative feedback is given with a larger amount as the mobility μbecomes higher. As a result, variations of the mobility μ in respectivepixels can be suppressed.

Specifically, when correction is made with the feedback amount ΔV₁ inthe pixel A having higher mobility μ, the drain-source current I_(ds) islargely decreased from I_(ds1)′ to I_(ds1). On the other hand, thefeedback amount ΔV₂ of the pixel B having lower mobility μ is small,therefore, the drain-source current I_(ds) is reduced from I_(ds2)′ toI_(ds2), which is not so large decrease. Consequently, the drain-sourcecurrent I_(ds1) of the pixel A becomes approximately equal to thedrain-source current I_(ds2) of the pixel B, therefore, variations ofthe mobility μ in respective pixels can be corrected.

Summarizing the above mentioned, when there exist the pixel A and thepixel B the mobility μ of which is different, the feedback amount ΔV₁ ofthe pixel A having larger mobility μ will be larger than the feedbackamount ΔV₂ of the pixel B having lower mobility μ. That is, the higherthe mobility μ of the pixel is, the larger the feedback amount ΔV is, aswell as the larger the decreased amount of the drain-source currentI_(ds) becomes.

Therefore, when the negative feedback is given to the gate-sourcevoltage V_(gs) with the feedback amount ΔV corresponding to thedrain-source current I_(ds) of the drive transistor 22, current valuesof the drain-source current I_(ds) in pixels having different mobilitiesμ are uniformed. As a result, variations of the mobility μ in respectivepixels can be corrected. That is, the processing of giving negativefeedback to the gate-source voltage V_(gs) of the drive transistor 22,namely, the storage capacitor 24 with the feedback amount (correctionamount) ΔV corresponding to current (drain-source current I_(ds))flowing in the drive transistor 22 is defined as the mobility correctionprocessing.

[1-3. Bottom-Emission Structure]

Incidentally, the organic EL display unit 10 having the aboveconfiguration applies a bottom-emission structure (method) as a methodof taking light emitted by the organic EL devices 21, in which light istaken from the backside of a transparent insulating substrate (forexample, a glass substrate) on which pixel circuits each including aTFT, a capacitor element and so on are formed. Here, an example of thebottom-emission structure will be explained.

FIG. 7 is a cross-sectional view showing an example of the bottomemission structure, and the same signs are put to the same portions asFIG. 2 in the drawing. In FIG. 7, a cross-sectional structure of aregion including the drive transistor 22 and the storage capacitor 24 isshown.

As shown in FIG. 7, the pixel circuit (drive circuit of the organic ELdevice 21) 20 including the drive transistor 22 and the storagecapacitor 24 is formed on a transparent insulating substrate, forexample, a glass substrate 71. More specifically, a gate electrode 221of the drive transistor 22, one electrode 241 of the storage capacitor24 and a lower-layer wiring 331 of the signal line 33 are formed on theglass substrate 71. The glass substrate 71 on which the pixel circuit 20is formed is generally referred to as a TFT substrate.

On the gate electrode 221 of the drive transistor 22 and one electrode241 of the storage capacitor 24, a semiconductor layer 222 where achannel region and source/drain regions of the drive transistor 22 areformed and the other electrode 242 of the storage capacitor 24 areformed through an insulating film 72. On the pixel circuit 20, a colorfilter 74 is directly, namely, formed in an on-chip manner through aninsulating planarization film 73. That is, the color filter 74 is anon-chip color filter.

On the insulating planarization film 73, an upper-layer wiring 332 ofthe signal line 33 is formed to be connected to the lower-layer wiring331. Additionally, an interlayer insulating film 75 is formed on thecolor filter 74 and an anode electrode 211 of the organic EL device 21is formed on the interlayer insulating film 75 pixel by pixel. Theorganic EL device 21 is provided at a recessed portion 76 _(A) of awindow insulating film 76 stacked on the interlayer insulating film 75.Furthermore, a cathode electrode 212 of the organic EL device 21 isformed in common with all pixels.

Here, the organic EL display unit 10 according to the applicationexample applies white organic EL devices emitting white light as theorganic EL devices 21 to thereby obtain, for example, light emissioncolors RGB of respective sub-pixels by the on-chip color filters 74. Asthe white organic EL device, for example, an organic EL device having atandem structure in which respective organic EL devices of RGB areformed in multi-stages, more specifically, in which respective lightemitting layers of RGB are stacked through connection layers.

As described above, the bottom-emission structure is a structure oftaking light emitted from the organic EL devices 21 from the backside ofthe glass substrate 71 on which the pixel circuits 20 are formed. In thebottom-emission structure, regions from which light is taken are limiteddue to existence of circuit components, wiring and the like on the glasssubstrate, therefore, the utilization ratio of emitted light of theorganic EL devices 21 is generally reduced as compared with atop-emission structure which takes light from the front side of thesubstrate.

However, in the organic EL display unit 10 according to the applicationexample, the pixel circuit 20 has a circuit configuration including twotransistors (22, 23) and one capacitor device (24). Accordingly, thenumber of transistors and the number of wirings formed on the TFTsubstrate (glass substrate 71) can be reduced, therefore, there is anadvantage that the utilization ratio of emitted light of the organic ELdevices 21 can be improved as compared with pixel circuits having threeor more transistors and so on when the bottom-emission structure isapplied.

[1-4. Problems Caused by Variation of Internal Resistance of a ColorFilter]

In the above organic EL display unit 10 having the bottom-emissionstructure, internal resistance of the color filter 74 may vary byreceiving light emission of a self-pixel when light emitted from theorganic EL device is transmitted through the color filter 74 accordingto a material of the color filter 74. The pixel circuit 20 is formedunder the color filter 74 in the bottom-emission organic EL display unit10, therefore, variation of internal resistance in the color filter 74affects circuit operations of the pixel circuit 20 when the internalresistance of the color filter 74 varies.

Problems caused by variation of internal resistance of color filter 74will be specifically explained with reference to an equivalent circuitof the color filter 74 shown in FIG. 8.

As shown in FIG. 8, the color filter 74 can be equivalently shown as aparallel circuit of a capacitive component C_(cf) and an impedancecomponent R_(cf). FIG. 8 shows extracted circuit components of the writetransistor 23 and the storage capacitor 24 in addition to the equivalentcircuit of the color filter 74, for simplifying the drawing.

In FIG. 8, “Ca” represents a capacitive component parasitizing betweenthe color filter 74 and the anode electrode 211 of the organic EL device21 (see FIG. 7) and “Cs” represents the storage capacitor 24. “Vs”represents the source potential of the drive transistor 22.

Here, the signal writing period and the light emission period areexplained in a separated manner which is different from theabove-described actual driving with reference to a timing waveformdiagram shown in FIG. 9 for making the explanation easy to understand.

As shown in FIG. 9, in the signal writing period, when the potential ofthe scanning line 31 (writing scanning signal) WS is transited to thehigh potential side and the write transistor 23 becomes in theconductive state in response to the transition, the signal voltageV_(sig) of the video signal is written to a node B. Here, the node B isa node to which the gate electrode of the drive transistor 22 and oneelectrode of the storage capacitor 24 are connected in common in thepixel circuit shown in FIG. 2.

When the signal voltage V_(sig) is written to the node B, the potentialV_(A) of a node A will be a potential defined by the followingexpression.

V _(A) =V ₁₁=(V _(sig) −V _(s))C _(cf)/(C _(cf) +C _(a))  (3)

During the non-emission period, namely, when light emission of aself-pixel is not received, impedance of the color filter 74 isextremely high, therefore, respective potentials V_(A) and V_(B) of thenodes A and B do not vary. However, when the organic EL device 21 emitslight and light is irradiated on the color filter 74, that is, whenlight emission of the self-pixel is received, leak current flows insidethe color filter 74 as the impedance (internal resistance) of the colorfilter 74 is reduced. Thus, the potential V_(A) of the node A isincreased, whereas the potential V_(E) of the node B is reduced.

As shown in the timing waveform diagram of FIG. 9, respective potentialsV_(A) and V_(E) of notes A and B vary so as to be the same potential inthe end. The final potential V₁₂ of the respective potentials V_(A) andV_(E) of notes A and B is defined by the following expression.

V ₁₂ =V _(s)+{(V _(s) −V _(s))(C _(cf) C _(s) +C _(s) C _(a) +C _(a) C_(cf))}/(C _(s) +C _(a))(C _(cf) +C _(a))  (4)

As described above, the internal resistance of the color filter 74varies by receiving light emission of the self-pixel and charges storedin the storage capacitor 24 are leaked due to the effect of theresistance variation, as a result, the potential V_(B) of the node B,namely, the gate potential Vg of the drive transistor 22 is reduced.Then, when the gate potential Vg of the drive transistor 22 is reduced,drive current to be supplied to the organic EL device 21 by the drivetransistor 22 is reduced as compared with the case where the internalresistance of the color filter 74 does not vary, therefore, lightemission luminance of the pixel 20 is largely reduced.

2. Explanation of an Embodiment

Consequently, the organic EL display unit 10 having the bottom-emissionstructure (method) applies the following structure for suppressingadverse effect caused by variation of internal resistance of the colorfilter 74 with respect to circuit operations of the pixel circuit 20.

That is, in the organic EL display unit 10 configured by applying thebottom-emission structure and being provided with the color filter onthe pixel circuit 20, metal wiring is formed so as to surround theperiphery of the color filter 74. The metal wiring is set to the anodepotential of the organic EL device 21.

The color filter 74 can be equivalently shown as the parallel circuit ofthe capacitive component C_(cf) and the impedance component R_(cf) asdescribed above. Then, when the periphery of the color filter 74 issurrounded by the metal wiring set to the anode potential, bothterminals of the equivalent circuit of the color filter 74 haveelectrically the same potential. Therefore, even when the internalresistance of the color filter 74 varies by receiving light emission ofthe self-pixel, the variation of the internal resistance of the colorfilter 74 does not affect the circuit operations of the pixel circuit asboth terminals of the equivalent circuit have the same potential.

[2-1. Pixel Configuration According to the Embodiment]

Hereinafter, the pixel configuration of an organic EL display unitaccording to the embodiment will be specifically explained withreference to FIG. 10 to FIG. 12.

FIG. 10 is a plan view showing an example of a pixel structure in theorganic EL display unit according to the embodiment. FIG. 11 is an arrowcross-sectional view taken along A-A′ line of FIG. 10 and FIG. 12 is anarrow cross-sectional view taken along B-B′ line of FIG. 10. In FIG. 10to FIG. 12, the same signs are put to portions equivalent to FIG. 2 andFIG. 7.

The organic EL display unit according to the embodiment has thebottom-emission structure in the pixel 20 in the same manner as the caseof the organic EL display unit 10 according to the above applicationexample. The bottom-emission structure of the pixel 20 is basically thesame structure as the bottom emission structure shown in FIG. 7.

Specifically, as shown in FIG. 11 and FIG. 12, the gate electrode 221 ofthe drive transistor 22, one electrode (hereinafter referred to as“lower electrode”) 241 of the storage capacitor 24 and the lower-layerwiring 331 of the signal line 33 are formed on, for example, the glasssubstrate 71 called the TFT substrate. As a material for the gateelectrode 221 of the drive transistor 22, one electrode 241 of thestorage capacitor 24 and the lower-layer wiring 331 of the signal line33, for example, molybdenum (Mo) and the like can be used.

On the gate electrode 221 of the drive transistor 22 and one electrode241 of the storage capacitor 24, the semiconductor layer 222 where thechannel region and the source/drain regions of the drive transistor 22are formed and the other electrode (hereinafter referred to as “upperelectrode”) 242 of the storage capacitor 24 are formed through theinsulating film 72. On the pixel circuit 20 including the drivetransistor 22 and the storage capacitor 24, the color filter 74 isformed directly, namely, as the on-chip color filter through theinsulating planarization film 73.

On the insulating planarization film 73, the upper-layer wiring 332 ofthe signal line 33 and a contact 223 portion of the transistor 22 areformed. As a material for the upper-layer wiring 332 of the signal line33 and the contact portion 223 of the transistor 22, for example,aluminum (A1) and the like can be used.

Additionally, the interlayer insulating film 75 is formed on the colorfilter 74 and the anode electrode 211 of the organic EL device 21 isformed on the interlayer insulating film 75 pixel by pixel. The organicEL device 21 is provided at the recessed portion 76 _(A) of the windowinsulating film 76 stacked on the interlayer insulating film 75. Theorganic EL device 21 is, for example, the white organic EL device, andthe cathode electrode 212 thereof is formed in common with all pixels.

Particularly apparent from FIG. 10, the signal line 33 including thelower-layer wiring 331 and the upper-layer wiring 332 is arranged on theleft-end side in the pixel (pixel circuit) 20 along a longitudinaldirection of the pixel 20. The lower-layer wiring 331 and theupper-layer wiring 332 are electrically connected by contact portions333 and 334 at two points in the pixel 20.

The power supply line 32 is wired on the top-end side in the pixel 20along a lateral direction of the pixel 20. The drive transistor 22 isformed in the vicinity of the power supply line 32. The drive transistor22 includes the gate electrode 221 formed on the glass substrate 71 andthe semiconductor layer 222 to be the channel region and thesource/drain regions which are formed above the gate electrode 221through the insulating film 72 as described above.

In the drive transistor 22, the gate electrode 221 is integrally formedwith the lower electrode 241 of the storage capacitor 24. Onesource/drain region of the semiconductor layer 222 is electricallyconnected to the upper electrode 242 of the storage capacitor 24 by acontact portion 224. The other source/drain region of the semiconductorlayer 222 is electrically connected to the power supply line 32 throughthe contact portion 223.

The storage capacitor 24 configured by using the insulating film 72 as adielectric and by sandwiching the insulating 72 by the lower electrode241 and the upper electrode 242 is formed on the right-end side of thepixel 20 over a large region along the longitudinal direction of thepixel 20. In the storage capacitor 24, a capacitance value is defined byan area of a region where the lower electrode 241 faces the upperelectrode 242, a distance between both electrodes 241 and 242 anddielectric constant of the insulating film 72.

The scanning line 31 is wired along the lateral direction of the pixel20 on the lower-end side in the pixel 20. The write transistor 23 isformed in the vicinity of the scanning line 31. The write transistor 23includes a gate electrode 231 formed on the glass substrate 71 and asemiconductor layer 232 to be a channel region and source/drain regionswhich are formed above the gate electrode 231 through the insulatingfilm 72.

In the write transistor 23, the gate electrode is electrically connectedto the scanning line 31 by a contact portion 233. One source/drainregion of the semiconductor layer 232 is electrically connected to thesignal line 33 by a contact portion 234. The other source/drain regionof the semiconductor layer 232 is electrically connected to the lowerelectrode 241 of the storage capacitor 24 through a contact portion 235,a metal wiring 236 and a contact portion 237.

The lower electrode 241 of the storage capacitor 24 is integrally formedwith the gate electrode 221 of the drive transistor 22 as describedabove. Thus, when the other source/drain region of the write transistor23 is connected to the lower electrode 241 of the storage capacitor 24,the other source/drain region of the write transistor 23 is electricallyconnected to the gate electrode 221 of the drive transistor 22.

In the pixel 20, the organic EL device 21 is formed at the centralportion surrounded by the signal line 33 on the left side, the storagecapacitor 24 on the right side, the power supply line 32 on the upperside and the scanning line 31 on the lower side, namely, in the recessedportion 76 _(A) of the window insulating film 76 in a state of avoidingthe drive transistor 22. The anode electrode 211 of the organic ELdevice 21 is electrically connected to the other source/drain region ofthe drive transistor 22 and the upper electrode 242 of the storagecapacitor 24 by the contact portion 224.

The color filter 74 is formed under the organic EL device 21 along anopening of the recessed portion 76 _(A) of the window insulating film 76in a state of avoiding the drive transistor 22. In FIG. 10, the colorfilter 74 is shown by a dashed dotted line for differentiating the colorfilter from other components. A metal wiring 77 is formed on theinsulating planarization film 73 so as to surround the periphery of thecolor filter 74. In FIG. 10, the metal wiring 77 is shown with hatching.

It is preferable that the metal wiring 77 is formed along a peripheralportion of the color filter 74. When the metal wiring 77 is formed alongthe peripheral portion of the color filter 74, a function as a lightshielding layer which shields light between pixels can be given to themetal wiring 77. It is preferable that the metal wiring 77 is formed soas to overlap with the peripheral portion of the color filter 74.

Because, the effects of steps to be generated in the peripheral portionin a tapered state at the time of forming the color filter 74 can besuppressed by the overlapping. In this case, the effects of the taperedsteps can be positively suppressed by forming the metal wiring 77 so asto overlap with the peripheral portion of the color filter 74 by thethickness of a film of the color filter 74 or more.

The metal wiring 77 is set to the anode potential of the organic ELdevice 21. In the present embodiment, the metal wiring 77 iselectrically connected to one source/drain region of the drivetransistor 22 by the contact portion 224. Therefore, the metal wiring 77can be also defined as wiring of one source/drain region of the drivetransistor 22.

Additionally, the anode electrode 211 of the organic EL device 21 andone source/drain region of the drive transistor 22 are connected by thecontact portion 224 as described above, therefore, the metal wiring 77is set to the anode potential of the organic EL element 21 through thecontact portion 224.

[2-2. Operation and Effect of the Embodiment]

As described above, the metal wiring 77 is formed so as to surround theperiphery of the color filter 74 in the organic EL display unit 10having the bottom-emission structure. Then, the following operation andeffect can be obtained by setting the metal wiring 77 to the anodepotential of the organic EL device 21 and shielding the color filter 74.

That is, when the periphery of the color filter 74 is surrounded by themetal wiring 77 set to the anode potential of the organic EL device 21to thereby shield the color filter 74, both terminals of the equivalentcircuit of the color filter 74 will have electrically the samepotential. The metal wiring 77 set to the anode potential of the organicEL device 21 can be referred to as shielding wiring. As described above,the color filter 74 can be equivalently shown as the parallel circuit ofthe of the capacitive component C_(cf) and the impedance componentR_(cf).

The potential of the metal wiring 77 surrounding the periphery of thecolor filter 74 is the anode potential of the organic EL device 21,therefore, both terminals of the equivalent circuit of the color filter74 are both connected to the anode electrode of the organic EL device 21as shown in FIG. 13 when seen from the aspect of the circuit. Therefore,even when light of the self-pixel is irradiated on the color filter 74and the internal resistance of the color filter 74 varies, charges arenot exchanged with the storage capacitor 24 positioned under the colorfilter 74 as both terminals of the equivalent circuit have the samepotential.

That is, when the internal resistance of the color filter 74 varies,charges stored in the storage capacitor 24 are not leaked by the effectof variation. Therefore, the gate potential Vg of the drive transistor22 is not reduced due to variation of the internal resistance of thecolor filter 74. As a result, reduction of light emission luminance canbe suppressed when the internal resistance of the color filter 74varies, therefore, good display images can be obtained.

3. Application Example

In the above embodiment, the case where the drive circuit of the organicEL device 21 basically has the circuit configuration including twotransistors which are the drive transistor 22 and the write transistor23 has been explained as the example, however, the present disclosure isnot limited to the above circuit configuration.

For example, the present disclosure can be applied to pixelconfigurations having various circuit configurations such as a circuitconfiguration in which a light-emission control transistor connected inseries to the drive transistor 22 is included while the potential of thepower supply line 32 is fixed, and light emission/non-light emission ofthe organic EL device 21 is controlled by the light-emission controltransistor.

As described above, in the organic EL display unit applying thebottom-emission structure, it is preferable, in the light of theutilization ratio of light emission of the organic EL device 21, toapply the circuit configuration of using two transistors as pixeltransistors as the number of circuit components can be reduced asdescribed above.

Also in the present disclosure, the case where the white organic ELdevice is used as the organic EL device 21 has been explained as anexample, however, the present disclosure is not limited to the case.That is, in an organic EL display unit using organic EL devices ofrespective light emission colors RGB as the organic EL devices 21, thecolor filters may be used, for example, for increasing color purity.Thus, the present disclosure can be applied to all organic EL displayunits applying the bottom-emission structure and using the color filter.

4. Electronic Apparatus

The above-described organic EL display unit according to the embodimentof the present disclosure can be applied to display sections (displayunits) of electronic apparatuses in various fields in which videosignals inputted to the electronic apparatus or video signals generatedin the electronic apparatus are displayed as images or video. As anexample, the organic EL display unit can be applied to display sectionsof various electronic apparatuses shown in FIG. 14 to FIGS. 18A to 18G,for example, a digital camera, a notebook personal computer, portableterminal devices such as a cellular phone, a video camera and so on.

As described above, when the organic EL display unit according to theembodiment of the present disclosure is used as display sections ofelectronic apparatuses in various fields, thereby improving imagequality of display in various types of electronic apparatuses. That is,as apparent from the explanation of the embodiment, the organic ELdevice unit according to the embodiment of the present disclosure cansuppress the reduction of light emission luminance when the internalresistance of the color filter varies. Therefore, good display imageswith high image quality can be obtained in various types of electronicapparatuses.

The organic EL device according to the embodiment of the presentdisclosure includes a module-type device with a sealed configuration. Asan example, a display module formed by bonding a counter portion made oftransparent glass and the like to the pixel array section corresponds tothis type. The display module may also be provided with a circuit unit,a FPC (flexible printed circuit) and so on for inputting/outputtingsignals and so on to the pixel array section from the outside.

Specific examples of electronic apparatuses to which the presentdisclosure is applied will be explained as follows.

FIG. 14 is a perspective view showing appearance of a television set towhich the present disclosure is applied. The television set according tothe present application example includes a video display screen unit 101having a front panel 102, a filter glass 103 and so on, which isfabricated by using the organic EL display unit according to theembodiment of the present disclosure as the video display screen unit101.

FIGS. 15A and 15B are perspective views showing appearance of a digitalcamera to which the present disclosure is applied. FIG. 15A is aperspective view seen from the front side and FIG. 15B is a perspectiveview seen from the back side.

The digital camera according to the application example includes a lightemitting unit 111 for flash, a display unit 112, a menu switch 113, ashutter button 114 and so on, which is fabricated by using the organicEL display unit according to the embodiment of the present disclosure asthe display unit 112.

FIG. 16 is a perspective view showing appearance of a notebook personalcomputer to which the present disclosure is applied. The notebookpersonal computer according to the application example includes akeyboard 122 operated when inputting characters and so on in a body 121,a display unit 123 displaying images and so on, which is fabricated byusing the organic EL display unit according to the embodiment of thepresent disclosure as the display unit 123.

FIG. 17 is a perspective view showing appearance of a video camera towhich the present disclosure is applied. The video camera according tothe application example includes a body 131, a lens 132 for imagingsubjects on a side surface facing the front, a start/stop switch 133used at the time of imaging, a display unit 134 and so on, which isfabricated by using the organic EL display unit according to theembodiment of the present disclosure as the display unit 134.

FIGS. 18A to 18B are appearance views of a portable terminal device, forexample, a cellular phone device to which the present disclosure isapplied. FIG. 18A is a front view in an opened state, FIG. 18B is a sideview thereof, FIG. 18C is a front view in a closed state, FIG. 18D is aleft-side view,

FIG. 18E is a right-side view, FIG. 18F is an upper surface view andFIG. 18G is a bottom surface view. The cellular phone device accordingto the application example includes an upper casing 141, a lower casing142, a connection portion (a hinge portion in this case) 143, a display144, a sub-display 145, a picture light 146, a camera 147 and so on. Thecellular phone device according to the embodiment the present disclosureis fabricated by using the organic EL display unit according to theembodiment of the present disclosure as the display 144 or thesub-display 145.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An organic EL display unit comprising: asubstrate; a pixel circuit; an organic EL device configured to emitlight to the substrate and formed between an anode electrode and acathode electrode; a color filter formed on the pixel circuit; and ametal wiring formed on a peripheral portion surrounding the colorfilter, wherein the metal wiring is connected to an anode electrode. 2.The organic EL display unit according to claim 1, wherein the metalwiring is formed so as to overlap with the color filter.
 3. The organicEL display unit according to claim 2, wherein the metal wiring overlapswith the color filter by the thickness of a film of the color filter ormore.
 4. The organic EL display unit according to claim 1, wherein thepixel circuit includes a write transistor; a storage capacitor storing asignal voltage written by the write transistor; a drive transistordriving the organic EL device based on a stored voltage of the storagecapacitor.
 5. The organic EL display unit according to claim 1, whereinthe metal wiring is formed so as to surround the color filter.
 6. Theorganic EL display unit according to claim 1, wherein the organic ELdevice is configured to emit white light.